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Cone Rod Dystrophy Type 1 /Rod Cone Dysplasia Type 1b    

crd1/rcd1b Test                                Code 306

Test Pricing

For breeds: American Staffordshire Terrier & American Pit Bull Terrier

Rod Cone Dysplasia Type 1b (rcd1b), previously named CRD1, is an early-onset form of retinal degeneration that is characterized by the loss of rods and cones, the cells in the retina that are responsible for vision. In affected dogs, severe visual impairment is evident when they are very young, by about 3-6 months of age. The retinal degeneration progresses quickly and usually results in complete blindness when dogs are in their early adulthood.

*N.B. A comment regarding the nomenclature of this disease and test from Dr. Gus Aguirre, one of the senior scientists involved in the initial characterization and subsequent investigations of this disease as well as in the mutation's identification: "The disease was previously considered a cone-rod dystrophy (crd1) based on incorrect phenotype ascertainment using ERG (1). The term crd1 should no longer be used to refer to the disease. In affected dog there is evidence of vision loss at an early age with severe retinal degeneration and complete blindness by early adulthood, and ophthalmoscopic diagnosis of advanced retinal degeneration by 1 year of age. The disease is caused by a mutation in the PDE6B gene, with clinical abnormalities similar to what is found in rcd1-affected Irish Setters, and rcd1a affected Sloughis. The disease is more appropriately classified as rod-cone dysplasia 1b(rcd1b)."

crd1/rcd1b Test:
A small deletion in PDE6B gene has been identified that is associated with the rcd1b disease in the American Staffordshire Terrier breed (2). crd1/rcd1b is inherited in an autosomal recessive mode, meaning that dogs of both sexes are equally affected when they inherit two copies of the mutation, one from each parent.

The DNA-based crd1/rcd1b test allows to determine genotype of a tested dog as being:

NORMAL - the dog has two copies of the normal gene and it is not going to develop early-onset retinal degeneration caused by the mutation in the PDE6B gene.

CARRIER - the dog has one copy of the normal gene and one copy of the mutation. The dog will not develop clinical signs of the rcd1b disease but it will transmit the mutation to about 50% of its progeny.

AFFECTED - the dog has two copies of the PDE6B mutation and will develop the early-onset retinal degeneration caused by the mutation.

Testing/Breeding Recommendations:
The great value of the DNA test is that it allows detection of carriers of one copy of the mutation. These dogs do not show clinical signs of the disease but they can pass the mutation on to their offspring. In order to avoid producing affected offspring, carriers of the rcd1b mutation should never be bred to other carriers or to affected dogs (see chart below).

Expected results for breeding strategies using the
crd1/rcd1b test
Parent 1
Genotype
Parent 2 Genotype
Normal/ClearCarrierAffected
Normal/ClearAll = Normal/Clear1/2 = Normal/Clear
1/2 = Carrier
All = Carrier
Carrier1/2 = Normal
1/2 = Carrier
1/4 = Normal/Clear
1/2 = Carrier
1/4 = Affected
1/2 = Carrier
1/2 = Affected
Affected All = Carrier
1/2 = Carrier
1/2 = Affected
All = Affected

This table highlights in yellow the breedings that will NOT produce rcd1b-affected pups. These breedings include at least one parent proven "Normal/Clear" by the OptiGen rcd1b test. All other combinations are at risk of producing crd1/rcd1b-affected pups.

Research leading to the discovery of the crd1/rcd1b mutation was conducted at Cornell University and the University of Pennsylvania, with collaboration by OptiGen.

References:

1. Kijas, JW, Zangerl B, Miller B, Nelson J, Kirkness EF, Aguirre GD, Acland GM. 2004.Cloning of the canine ABCA4gene and evaluation in canine cone-rod dystrophies and progressive retinal atrophies. Mol Vis. Mar 29;10:223-32

2. Goldstein O, Mezey JG, Schweitzer PA, Boyko AR, Gao C, Bustamante CD, Jordan JA, Aguirre GD, Acland GM. 2013. IQCB1 and PDE6B mutations cause similar early onset retinal degenerations in two closely related terrier dog breeds. Invest Ophthalmol Vis Sci. Oct 25; 54(10):7005-19.

 

 

 


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Tel: 607 257 0301 · Fax: 607 257 0353 · email: genetest@optigen.com or optigen@clarityconnect.com
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